Internal filter

ABSTRACT

An internal filter that may be installed or removed from the outside of the housing. The internal filter may also cooperate with an inlet passage for a charge pump.

BACKGROUND OF THE INVENTION

This invention relates generally to hydrostatic transmissions andsimilar hydraulic devices. This invention also relates to the design offilters and more particularly, to the design of an internal filter usedwith such devices and to the design of a fluid flow path from the filterto an inlet of a hydrostatic transmission center section, eitherdirectly or by means of a charging pump.

DESCRIPTION OF THE PRIOR ART

While it is known to provide an oil filter in conjunction withhydrostatic transmissions, providing such oil filters often addscomplexity to a hydraulic device and may also create applicationdifficulties, as some filters in compact hydrostatic devices are locatedbelow the center section and reduce the ground clearance or causeinstallation difficulties because of the volume required for the filter.Further, the addition of a charging pump adds to the complexity of theinternal components and increases the difficulty of effectivelypositioning a filter.

Filters of various external and internal configurations for use inconnection with hydrostatic transmissions and pumps are well known inthe industry. For example, U.S. Pat. No. 5,613,409 shows an unlabeledinternal filter attached to the bottom of a center section. This filteris smaller than an opening formed in the housing that is covered by acap. Thus, by removing the cap, the filter may be accessed and removedwithout significant disassembly of the unit. Other internal filters thatare currently used in the industry require significant disassembly ofthe transaxle before the filter may be removed or replaced. Similarly,externally attached filters are also known in the industry. However,external filters may be exposed to debris and risk being damaged. Theymay also expand the external volume required of the device to which theyare attached. Lastly, fluid must travel into and out from an externalfilter, requiring a relatively complex interface, and an increased riskof leakage.

While the aforementioned filters work for their intended purpose, thereis a need to reduce the complexity associated with replacing internalfilters and the risk of leakage associated with external filters.

SUMMARY OF THE INVENTION

The invention shown herein comprises an internal filter that may beinstalled or removed from the outside of the housing. The internalfilter may also cooperate with an inlet passage for a charge pump.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forthillustrative embodiments and are indicative of the various ways in whichthe principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a transaxle incorporating the presentinvention.

FIG. 2 is a side elevational view of the transaxle of FIG. 1.

FIG. 3 is a bottom plan view of the transaxle of FIG. 1.

FIG. 4 is a top plan view of the transaxle of FIG. 1.

FIG. 5 is a section view of the transaxle taken along the lines 5—5 inFIG. 4.

FIG. 6 is a perspective view of the present invention installed within ahousing cover.

FIG. 7 is a bottom view of the housing cover shown in FIG. 6.

FIG. 8 is a top view of the housing cover shown in FIG. 6.

FIG. 9 is a section view of the housing cover shown in FIG. 6 along thelines 9—9 in FIG. 8.

FIG. 10 is view similar to that shown in FIG. 9 showing an alternativedesign of the housing cover shown in FIG. 9.

FIG. 11 is a section view of the housing cover shown in FIG. 6 along thelines 11—11 in FIG. 8.

FIG. 12 is a view similar to that shown in FIG. 11 showing a secondembodiment of an internal filter.

FIG. 13 is a perspective view of the internal filter shown in FIGS.1-11.

FIG. 14 is a perspective view of the internal filter shown in FIG. 12.

FIG. 15 is a section view of a third embodiment of an internal filterinstalled within a housing cover similar to that shown in FIG. 6.

FIG. 16 is a section view of a fourth embodiment of an internal filterinstalled within a housing cover similar to that shown in FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 show a hydrostatic transaxle 10 in which the present inventionmay be incorporated. Generally, hydrostatic transaxles operate on theprincipal of an input shaft 12 driving a hydraulic pump 14 and causingdisplacement of fluid to a hydraulic motor 16. As pump 14 rotates itdisplaces fluid through porting located in the center section (asdescribed below) to drive motor 16. Input shaft 12 is also coupled to aprime mover such as a vehicle engine (not shown) either directly or bymeans of a belt driving a pulley 18. Input shaft 12 may optionallyinclude a cooling fan 20.

For displacing fluid to motor 16, hydraulic pump 14 shown in FIG. 5 isprovided; this hydraulic pump may be an axial piston pump, whichcontains pistons 22. To cause pistons 22 to displace fluid to motor 16,swash plate 24 may be moved by control arm 25. Control arm 25 may beconnected to various types of mechanical, electric, hydraulic orpneumatic mechanisms capable of causing the movement of swash plate 24.

Although this description describes a hydrostatic transaxle containingan axial piston pump and axial piston motor, it should be appreciatedthat the disclosed embodiments may also be used in conjunction with avariety of hydraulic devices such as stand-alone hydraulic pumps ormotors that may be of other configurations, such as radial piston,gerotor, and the like. For a more detailed description of the principlesof operation of a hydrostatic transmission, the reader is referred toU.S. Pat. Nos. 5,314,387, and 6,322,474, which are incorporated hereinby reference in their entirety. In addition, motor 16 may exist as anindependent unit in a separate housing.

For driving axle shaft 32, motor 16 drives output shaft 30 that may beassociated with other components such as gears. It should be understoodthat the output shaft may be accessible from the exterior of housing 28and that motor 16 may drive two or more axle shafts by a variety ofmeans, including a differential. Both pump 14 and motor 16 areoperatively mounted on a center section 17, which contains hydraulicporting therein. It should also be understood by those with skill in theart that there are multiple center section configurations and that thisinvention may be readily configured to operate with all known centersections and center section equivalents.

To aid in providing additional fluid to the porting that connects pump14 and motor 16, a charge pump 34 may be provided. This additional fluidis necessary to makeup for fluid that may be lost due to expectedleakage from pistons 22, under pump 14, motor 16 or other locations,such as bleeds and valves. An exemplary charge pump 34 is shown in FIGS.2, 3, and 5. A filter may be included on an inlet to the porting betweenpump 14 and motor 16, including an inlet to charge pump 34 to increasethe operational life of the hydraulic components.

FIG. 5 shows a housing 28 with a housing cover or portion 36, a sump 29and a center section 17 positioned within sump 29. An inlet manifold 52may be formed with or secured to center section 17 to provide a fluidgallery. For allowing fluid to flow between sump 29 and inlet manifold52, housing cover 36 may include a fluid inlet or inlet passage 44. Itshould be understood by those with skill in the art that the shape andcomposition of the various housing elements herein described are notcritical to the invention and that this invention could be used with awide variety of housing configurations.

For removing impurities from fluid traveling from sump 29 (also referredto herein as the first fluid side) to inlet manifold 52 (also referredto herein as the second fluid side), a filter 38 may be provided. FIGS.6, 7, 8, 9, and 11 show housing cover 36 with an opening 37, which islocated between sump 29 and inlet passage 44 and which is capable ofreceiving a filter. Therefore, filter 38 may be installed within opening37 to remove impurities from fluid as described above. It should beappreciated that filter 38 may be easily installed and removed fromoutside of housing 28, without requiring the removal of housing cover 36or other components.

Filter 38 is comprised of a filter body 39 having a first end 39 a, asecond end 39 b and a sidewall 39 c, which joins first end 39 a andsecond end 39 b. One or more portions of side wall 39 c of filter 38 arecomprised of filter media 40. Filter media 40 allows fluid to passthrough it, while simultaneously removing impurities therefrom. Fluid ispulled from sump 29 through filter media 40 by the action of hydraulicpump 14 or charge pump 34. This fluid then travels from filter media 40into second end 39 b of filter 38. The second end 39 b of filter 38 isfurther comprised of a first support section 41 a, a second supportsection 41 b and a mid section 41 c connecting first and second supportsections 41 a, 41 b. For allowing fluid to flow from the first fluidside to the second fluid side, first support section 41 a includes apassage 43 and mid section 41 c includes at least one aperture. Passage43 is in fluid communication with aperture 51 and the second fluid side,while aperture 51 is also in fluid communication with inlet passage 44.It should be understood that filter 38 may include a single aperture 51or a plurality of apertures 51.

Thus, fluid can flow from the first fluid side through filter media 40in filter 38, through passage 43 in first support section 41 a, throughaperture 51 in mid section 41 c and into inlet passage 44, which isformed in housing cover 36. As shown in FIGS. 5 and 9, the fluidcontinues to travel through inlet passage 44 to charge pump passage 46,which may be connected to charge pump 34. Since inlet passage 44 ispreferably formed after housing cover 36 has been molded, plug 45 isused to seal inlet passage 44. Housing cover 36 may also be designed toinclude inlet passage 44 as part of the molding process, therebyalleviating the need for plugging any portion of inlet passage 44.

As shown in FIGS. 11 and 13, for securely mounting filter 38 to housing36 within opening 37, first support section 41 a and second supportsection 41 b are designed to fit within opening 37 and to assume amating relationship with housing cover 36. Opening 37 may also bedesigned to have a first end 37 a located on the exterior surface ofhousing cover 36 and a second end 37 b located on the interior surfaceof housing cover 36 where the diameter of first end 37 a is larger thanthe diameter of the second end 37 b. To achieve a mating relationshipwith housing cover 36, second support section 41 b of filter 38 isdesigned to be proportional to the diameter of first end 37 a of opening37 and first support section 41 a is designed to be proportional tosecond end 37 b of opening 37. It should also be appreciated by thosewith skill in the art that first support section 41 a and second supportsection 41 b may be removably attached to housing cover 36 by usingcommonly known means, such as threaded relationships, snap fittings orother attachment means.

In a configuration that does not require a charge pump, charge pumppassage 46 may be eliminated and replaced by passage 48, as shown inFIG. 10. Therefore, passage 48 would lead directly to inlet manifold 52and hydraulic fluid would be available to center section 17 via passage48.

As shown in FIGS. 6, 7, and 8 in a configuration with a charge pump 34,hydraulic fluid under pressure would be forced into passage 50 by chargepump 34, and thus into inlet manifold 52 where the pressurized fluidwould be available to center section 17. Inlet manifold 52 may be sealedin its interface with center section 17 to form a pressure container andalso to prevent the entry of unfiltered fluid. In configurationsincluding a charge pump, such as charge pump 34, there may also be ameans of relieving excess pressure within inlet manifold 52, oftencalled a charge relief. The charge relief may be provided as part ofcover 36, as part of inlet manifold 52, as part of center section 17, ormay be formed in or between one or more of these components, as aleakage path.

To prevent leakage of fluid from the intersection of filter 38 and cover36, filter 38 mounts within cover 36 and o-ring 54 seals filter 38 tohousing cover 36 in an SAE straight thread configuration, as shown inFIG. 11. In order to prevent fluid from bypassing filter media 40, firstsupport section 41 a of filter 38 may be provided with an interfacesurface 56 to contact a similarly configured surface 58 located withincover 36. Thus, when filter 38 is mounted to cover 36, surface 56tightens against surface 58 and forms a seal sufficient to preventcontaminants from passing between these two surfaces. Depending on thetolerances of the associated components, the lower portion 60 of filter38 may not contact surface 62 of housing 36. However, the tolerances oflower portion 60 and contact surface 62 are set such that o-ring 54 willprovide a seal to prevent leakage from the housing, while also providingsufficient contact between surfaces 56 and 58 to prevent contaminantsfrom passing through the interface between surfaces 56 and 58.

As shown in FIGS. 11 and 13, filter 38 includes longitudinal supports 64and radial support 66. These portions of filter 38 provide strength andstructure to support filter media 40 and paths for plastic flow duringmolding. To allow a portion of the mold to be extracted after filter 38is formed, the end of filter 38 may also includes an opening 68. Toseparate the internal portions of filter 38 from the external portionsof filter 38 opening 68 is covered by cap 70, which may interlock with aridge 72 formed on filter 38 or may be attached by means of an adhesiveor sealant or other means known in the art. A second embodiment of thepresent invention is shown in FIGS. 12 and 14. In this embodiment, ano-ring 76 provides a seal between filter 138 and housing cover 136 toprevent fluid from flowing from sump 29 to inlet manifold 52 withoutbeing pulled through filter media 40. This configuration also permitsfilter 138 to be fully tightened against housing 136, as compared to thefirst embodiment shown in FIG. 11. The embodiment shown in FIGS. 12 and14 also includes o-ring 154 that functions similarly to o-ring 54 of thefirst embodiment.

As shown in FIG. 14, for removing ferrous particles from the fluid, amagnet 74 may be located at one or more locations on filter 38. Magnet74 may be affixed to filter 38 with an adhesive or a variety ofmechanical techniques, such as by threaded attachment, snap fitting orpress fitting of magnet 74 to filter 38. Removing these particles mayextend the life of the filter.

FIG. 15 discloses a third embodiment of the internal filter having a capportion 78 and a media portion 80. To compress gasket 84 and maintainmedia portion 80 in position, spring 82 provides a force against mediaportion 80. For removing ferrous impurities that pass through filtermedia 40, cap portion 78 may also include an internal magnet 86.

FIG. 16 discloses a fourth embodiment of the internal filter also havinga cap portion 278 and a media portion 280, but cap portion 278constrains media portion 280 longitudinally at one side while housing236 has a step 90 that constrains media portion 280 on the oppositeside. In addition, the close fit of media portion 280 within bore 237 ofcover 236 maintains the generally vertical orientation of media portion280. To assure fluid is pulled through media 40 of media portion 280,o-ring 88 provides a seal between media portion 280 and housing 236.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangement disclosed is meant to be illustrative only andnot limiting as to the scope of the invention, which is to be given thefull breadth of the appended claims and any equivalents thereof.

1. A hydraulic drive device comprising: a housing forming a sump and having an opening; a center section positioned within the sump and forming porting; an inlet passage formed within the housing to create a fluid inlet to the porting; a filter inserted through the opening and extending into the sump, the filter being located between the sump and the inlet passage and providing a fluid seal of the opening.
 2. The hydraulic drive device of claim 1, further comprising an input shaft, wherein the filter is generally cylindrical and extends in a direction generally parallel to the input shaft.
 3. The hydraulic drive device of claim 1, further comprising an output axle, wherein the filter is generally cylindrical and extends in a direction generally perpendicular to the output axle.
 4. The hydraulic drive device of claim 1, wherein the filter further comprises: a generally cylindrical body enclosing a volume, wherein the body comprises a plurality of openings that are in fluid communication with the sump; filter media covering the openings; a hole located at one end of the generally cylindrical body; a cap covering the hole; and a passage located at the other end of the generally cylindrical body that is in fluid communication with the openings and the fluid inlet to the porting.
 5. The hydraulic drive device of claim 4, wherein the filter comprises a surface that contacts the housing to restrict fluid flow between the sump and the fluid inlet at the point of contact between the surface and the housing.
 6. The hydraulic drive device of claim 4, wherein an o-ring is positioned between the filter and housing to restrict fluid flow between the sump and fluid inlet at the point of contact between the filter and the housing.
 7. The hydraulic drive device of claim 4, wherein the filter further comprises a magnet.
 8. The hydraulic drive device of claim 7, wherein the magnet is attached to the cap.
 9. A hydraulic drive device comprising: a housing forming a sump and having an opening; a center section positioned within the sump and forming porting; an inlet passage formed within the housing to create a fluid inlet to the porting; a filter inserted through the opening and extending vertically into the sump, the filter being located between the sump and the inlet passage; wherein the filter is secured within the housing so that one portion of the filter is within the sump, one portion of the filter provides a fluid seal with the housing, and one portion of the filter is exterior to the sump.
 10. The hydraulic drive device of claim 9, wherein the filter extends generally perpendicularly to the inlet passage.
 11. The hydraulic drive device of claim 9, wherein the filter further comprises: a first end, a second end and a generally cylindrical body joining the first end and the second end, the cylindrical body enclosing a volume and further comprising a plurality of openings that are in fluid communication with the sump; filter media covering the openings; and a passage located at the second end of the generally cylindrical body, wherein the passage is in fluid communication with the openings and the fluid inlet to the porting.
 12. The hydraulic drive device of claim 11, wherein the cooperation between the filter and the housing force fluid to enter the fluid inlet to the porting via the openings in the filter only.
 13. A hydraulic drive device comprising: a housing forming a sump and having an opening; a center section positioned within the sump and forming porting; an inlet passage formed within the housing to create a fluid inlet to the porting; an opening in the housing having a first end and a second end, wherein the first end opens at an exterior surface of the housing and has a first diameter, and the second end opens at an interior surface of the housing and has a second diameter smaller than the first diameter; and a filter having a portion with a diameter that is sized to fit within the second diameter and that extends through the second end of the opening into the sump, and another portion that is sized to fit within the first diameter and positioned within the first end of the opening.
 14. The hydraulic drive device of claim 13, wherein a cap covers the first end of the opening and provides a fluid seal.
 15. The hydraulic drive device of claim 14, wherein the cap locates the filter within the housing opening.
 16. The hydraulic drive device of claim 14, wherein a spring is located between the cap and the filter.
 17. The hydraulic drive device of claim 14, wherein a magnet is attached to the cap.
 18. The hydraulic drive device of claim 13, wherein a seal is positioned between the filter and the housing.
 19. The hydraulic drive device of claim 18, wherein the filter is generally perpendicular to the inlet passage.
 20. The filter as recited in claim 13, wherein the filter further comprises an o-ring positioned between the filter and the first end of the opening in the housing.
 21. The hydraulic drive device of claim 13, wherein the fluid inlet is connected to a charge pump.
 22. The hydraulic drive device of claim 21, wherein the charge pump is in fluid communication with a fluid manifold. 